Many downhole well systems use downhole flow control valves and other devices which are hydraulically actuated by double acting hydraulic pistons. For example, a downhole control valve may employ a double acting hydraulic piston to operate a moving sleeve which, in turn, controls the inflow or outflow of fluid with respect to the surrounding borehole and formation. Actuating fluid is supplied from a surface pressure source and routed downhole through two hydraulic control lines coupled with hydraulic control chambers on opposed sides of the actuating piston. One hydraulic line provides high-pressure fluid to a hydraulic control chamber on one side of the piston while the other hydraulic line evacuates an equivalent volume of low-pressure exhaust fluid from the hydraulic control chamber on the other side of the piston. However, if the flow of hydraulic actuating fluid into or out of either chamber is blocked, the system becomes hydraulically locked, e.g. the control valve cannot be actuated to a different flow position.